The present invention relates to an apparatus for forming perforations in the surfaces of wood beams as a preliminary step to the application of preservatives to the beams so as to improve absorption of the preservative by the wood, and in particular to the cleaning of the rotary drum wood incisors used in forming such perforations to prevent the accumulation of material between the incisor teeth.
The process of treating rough lumber with a selected preservative typically includes a preparatory step involving the perforation of the wood surfaces by sets of paired drums having outwardly protruding cutting teeth as taught, for example, in Toberg U.S. Pat. No. 4,137,956, the disclosure of which is hereby incorporated by reference. The teeth of such devices are located around the periphery of a plurality of incisor rings which are separated from one another by one or more spacer rings. In operation the space between these teeth becomes clogged with pitch, wood slivers and similar debris which interferes with the desired penetration of the teeth into the wood surface. Wood incisors of the prior art, such as that shown in Silcox U.S. Pat. No. 4,706,722, teach the use of a rotatable and freely-radially movable annular cleaning ring which surrounds each spacer ring and has an outside diameter which is at least equal to the outside diameter of the incisor ring plus the height of a tooth. In such prior art arrangements, when the teeth penetrate the wood surface the periphery of the cleaning ring is forced to project beyond the periphery of a segment of the incisor ring opposite the side of engagement with the wood. The effect is to push any accumulated substances outwardly from the teeth on this segment of the incisor ring periphery.
Such prior art devices employing sliding cleaning rings frequently fail to operate as a result of the accumulation of pitch and other debris on the cleaning rings which prevents them from moving radially. Also, such devices require replacement of the cleaning rings with rings of an alternative size when employing incisor rings with different sized teeth so as to maintain the correct functional projection of the cleaning rings beyond the periphery of the teeth. Such prior art devices also require cleaning rings fabricated from relatively expensive lower friction metals.
Therefore, a need exists for an apparatus for performing perforations on wood surfaces having a cleaning mechanism which will operate satisfactorily with a surface build-up of pitch and similar wood debris and which can be used in conjunction with a wide range of incisor rings having a variety of teeth sizes.